Is Sucralose—The Sweetener Most Commonly Known As Splenda—Really Safe?

That little yellow packet may not be so innocent. Sucralose—the no-calorie sugar substitute most commonly known by the brand name Splenda—has been found to cause a variety of harmful biological effects in the body, according to a recent research review published in the Journal of Toxicology and Environmental Health, Part B: Critical Reviews.

Early research said that sucralose passes through your GI tract undigested, so the theory was that it had little to no effect on you. But new studies show that sucralose is actually metabolized, says study coauthor Susan S. Schiffman, PhD, an adjunct professor at North Carolina State University. Enter a slew of problems, including:

Reduces good gut bacteria: Sucralose alters the amount and quality of those beneficial microbes that hang out in your belly (the same ones found in yogurt) by 50% or more. “Alteration in bacterial counts is associated with weight gain and obesity,” says Dr. Schiffman.

Makes meds less effective: Sucralose limits the absorption of therapeutic drugs, such as those for cancer and heart disease, rendering them less effective.

Releases toxins: Many people bake with Splenda to reduce the calories in a recipe, but sucralose decomposes during baking, which releases potentially toxic compounds called chloroproanols.

May alter your body's responses: Sucralose can alter insulin responses and blood sugar levels, has been associated with inflammatory bowel disease, and may even alter genes, the researchers note.

Now, let’s put the research in perspective. It was performed on rats, and rats are obviously not humans. However, the FDA’s approval of how much sucralose can be consumed safely is also based on rat studies, so it’s a fair comparison.

More: 288 Low-Sugar Snacks Under 100 Calories

The research also used amounts of that are approved for use in food, not megadoses, and some adverse effects from sucralose were seen at very low levels. For example, says Dr. Schiffman, drinking the equivalent of less than a diet soda a day was found to reduce good gut bacteria, and two diet sodas a day could limit drug absorption. (If you're addicted to your diet fix, these 7 Gross Facts About Diet Soda will make you rethink your habit.)

Other research published in Trends in Endocrinology & Metabolism in 2013 found that sugar substitutes with sucralose are linked to type 2 diabetes, heart disease, metabolic syndrome, and obesity. So if you want something sweet, your best option is regular sugar in moderation (not sucralose)—no more than 100 calories, or 6 added teaspoons a day, per the American Heart Association’s recommendations.

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